This invention relates generally to light engines for projection display systems, and more specifically to light engines for use with color imaging systems.
Typically, a light source is used for a light engine, enabling projection of images in a display system. As such, many types of light engines may provide light to project color images for a variety of projection display systems, including a color imaging system. An example of such a light engine is a collinear light engine that is shown in FIG. 1 in connection with a color imaging system 5 according to a prior art projection display system. In this example, the prior art system 5 utilizes a light source 10, such as an ultra high-pressure (UHP) lamp 10 to provide light. At the output region of the light source 10, a set of optical components may be disposed, forming an input light beam. The set of optical components may include an ultraviolet and infrared (UV-IR) filter 12, a light pipe homogenizer 14, a color switch or color wheel 16, and a lens 18 by way of one example. However, many of these optical components may have alternate forms. In the configuration shown in FIG. 1, a conventional polarizer, such as an output polarization analyzer 20 may serve to pass the light of a first polarization xe2x80x9cPxe2x80x9d while skipping or reflecting the light of a second polarization xe2x80x9cS.xe2x80x9d The color switch 16 in combination with the output polarization analyzer 20 may ideally pass red light through, for example, and selectably switch or alternate between either passing blue light and reflecting green light or passing green light and reflecting blue light.
The prior art system 5 may further include an imaging pre-filter, i.e., an RC1 filter 22 which is deployed in the output region of the lens 18. A polarization beam splitter (PBS) 24 with a first side facing the RC1 filter 22 may additionally be provided thereafter. In the same way, on a second side of the PBS 24, a quarter-wave (xcex/4, xcex being the wavelength) retarder 26 and a first spatial light modulator (SLM) 28 may be located. Yet another quarter-wave retarder 30 and a second SLM 32 may be provided on a third side of the PBS 24. In operation, an electronic drive may present to the first SLM 28 image data that alternates between blue and green image data, while the second SLM 32 may be presented only with red image data. A clean-up polarizer 38, and a projection lens 40 may be configured on a fourth side of the PBS 24 to provide an output beam based on a particular electronic drive, presenting image data in a specific format including a red-blue-green (RGB) format, as one example.
Taken together, the prior art system 5 may typically be said to include a light engine incorporating the elements 10, 12 and 14, a color switch subsystem including the elements 16, 18 and 20, an imaging subsystem or kernel comprising the elements 22 through 38, and a projection subsystem that includes element 40. In particular, the color switch subsystem may be said to have an input axis (AxisIKin) through the first side of the PBS 24, and the light source 10 which may be said to have an output axis (AxisLEout) through the light pipe homogenizer 14. Because the in put axis of the color switch subsystem is in a coaxial or a collinear orientation with respect to the output axis of the light source 10, the prior art system 5 is usually characterized as a collinear panel-based projection display system.
As such, for a host of projection display systems including a panel-based color imaging system depicted in FIG. 1, among other design features, contrast ratio is often a significant design feature. However, leakage of light with an incorrect polarization through the color switch 16 and the output polarization analyzer 20 typically contributes to the background leakage illumination, reducing the contrast ratio. For example, if the color switch 16 imperfectly switches between blue and green, some amount of the reflected color light may pass through to the first SLM 28 while it is still modulating the earlier passed color light.
In the prior art system 5, the color switch 16 while passing green light (on the left) may undesirably reflect blue light (on the right), causing the blue leakage light (BL) to appear in the output beam from the projection lens 40. Because of the architectural configuration of this system 5, imperfections in the operation of the output polarization analyzer 20 may further contaminate the output beam. The input filter (UV-IR filter 12) may also improperly reflect the xe2x80x9cSxe2x80x9d polarization green light (on the left, shown as a dashed line). As a result, this green light leakage may strike the first SLM 28 along with the xe2x80x9cPxe2x80x9d polarization green light, reflecting both the green light and leakage thereof into the output beam (shown as GL and G, respectively). Therefore, leakage of light with the incorrect polarization, onto the spatial light modulators and into the output beam may cause undesirable degradation of a projected image in a panel-based color imaging system.
Thus, there is a continuing need for better ways to configure light engines for use with projection display systems, especially in connection with color imaging systems.